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Modelling Chemical and Physical Processes of Wood and Biomass Pyrolysis

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Abstract

This review reports the state of the art in modeling chemical and physical processes of wood and biomass pyrolysis. Chemical kinetics are critically discussed in relation to primary reactions, described by one- and multi-component (or one- and multi-stage) mechanisms, and secondary reactions of tar cracking and polymerization. A mention is also made of distributed activation energy models and detailed mechanisms which try to take into account the formation of single gaseous or liquid (tar) species. Different approaches used in the transport models are presented at both the level of single particle and reactor, together with the main achievements of numerical simulations. Finally, critical issues which require further investigation are indicated.

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... 44 6.99 [41] Coats-Redfern (Geometric contraction) 250-400 5 36.53 9.06 [41] Coats-Redfern (Avarami-Erofe'ev) 250-400 5 15.73 5.53 [41] Coats-Redfern (Power Law) 250-400 5 9.70 5.53 [41] Modified [8] a: Referred to by the authors as the "linear regression method"; b: No temperature data were provided, just the variation with the conversion. c: Referred to by the authors as "based on Arrhenius equation", based on Mureddu et al. [44]. ...
... Energies 2022, 15,7240 a: Sourced from the aforementioned round-robin using the same equipment as that employed in the context of this work [4]. ...
... Energies 2022, 15,7240 3.5% ± 1.4% 5.8% ± 6.5% 8.8% ± 9.3% Free Order to All 2.9% ± 0.6% 5.3% ± 5.6% 8.1% ± 9.5% ...
Article
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Wheat straw is a renewable agricultural by-product that is currently underutilized in the production of bioenergy and bioproducts due to its high ash content, as well as high transport costs due to its low volumetric energy density. The thermogravimetric analysis of this material produces derivative curves with a single broad peak, making it difficult to identify the three conventional pseudo-components (cellulose, hemicellulose, and lignin), which is resolved using the second derivative to determine inflection points. Model-fitting methods and isoconversional methods were applied to determine the degradation kinetics of wheat straw at two different particle sizes, as well as that of a reference feedstock (beech wood), and the obtained values were used to divide the degradation curves to be compared to the experimental data. Seven different pyrolysis reaction networks from the literature were given a similar treatment to determine which provides the best estimation of the actual pyrolysis process for the case of the feedstocks under study. The impact of the potassium content in the feedstock was considered by comparing the original pathway with a modification dependent on the experimental potassium content and an estimated optimum value.
... The differential thermogravimetry analysis (DTG) results are shown in Figure 3. Pyrolysis of woods has been shown to involve the decomposition of three pseudo-components: hemi-cellulose, cellulose, and lignin. 31 The decomposition rate (or conversion rate) of each pseudo-component contributes to a total MLRs in Figure 3. In nitrogen (Figure 3(a)), the pyrolysis starts at ;500 K and reaches a shoulder at 550-600 K. Hemi-cellulose accounts for most of the decomposition process in this range. ...
... In nitrogen (Figure 3(a)), the pyrolysis starts at ;500 K and reaches a shoulder at 550-600 K. Hemi-cellulose accounts for most of the decomposition process in this range. 31 A successive peak occurs at 640-700 K. This peak corresponds to the main cellulose decomposition and is responsible for the largest volatile generation. ...
... The decompositions of hemi-cellulose and cellulose are known to be globally endothermic, whereas the lignin decomposition is exothermic. 31,32 In a previous work, Hostikka and Matala performed TGA and differential scanning calorimetry (DSC) on the same wood type (heating rates ranging from 2 to 20 K/min) in nitrogen. 32 Their TGA result at 10 K/min was plotted in Figure 3 for comparison. ...
Article
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Firebrand (ember) attack has been shown to be one of the key mechanisms of wildfire spread into wildland–urban interface communities. After the firebrands land on a substrate material, the ignition propensity of the material depends on not only the attributes (e.g. shape, size, and numbers) but also the distribution of the firebrands. To help characterize this process, this study aims to investigate the effects of gap spacing on the burning behaviors of a group of wooden samples. Experiments are conducted using nine wooden cubes, 19 mm on each side. These samples are arranged in a 3 × 3 square pattern on suspension wires and are ignited by hot coils from the bottom surface. The gap spacing (s) between the samples varies in each test (ranging from 0 to 30 mm). After ignition, the samples are left to burn to completion. The burning process is recorded using video cameras. Sample mass loss and temperatures are monitored during the flaming and smoldering processes. The results show that the flame height and the sample mass loss rate have non-monotonic dependencies on the gap spacing. When the gap spacing reduces, the flame height and the mass loss rate first increase due to enhanced heat input from the adjacent flames to each sample. When s ≤ 10 mm, flames from individual samples are observed to merge into a single large fire. As s further decreases, the air entrainment at the flame bottom decreases and the flame lift-off distance at the flame center increases, resulting in an increased flame height, decreased flame heat feedback to the solid samples, and a decreased mass loss rate. The decreased mass loss rate eventually leads to a decrease in the flame height as well. The gaseous flame height is correlated to the solid burning rate. The correlation generally follows previous empirical equations for continuous fire sources. For the smoldering combustion, compared to a single burning sample, the smoldering temperature and duration significantly increase due to the thermal interactions between adjacent burning samples. To help interpret the results of the burning experiments, thermogravimetric analysis is also performed in air and nitrogen, resulting in heating rates ranging from 10 to 100 K/min.
... Catalytic Effect of Inorganics AAEM such as K, Na, Ca, and Mg are inherent in MWB and alter their pyrolysis. Potassium salts are known catalysts during devolatilization and promote exothermic char formation [51,52]. It increases emissions of CO 2 , H 2 O, and CO (by favoring cracking reactions of tar [3]) and NH 3 (NO x precursor) [53]. ...
... For BP, SS, and AD, HoSTR is prominent from ≈565 • C. However, the exact endset of HoSTR can vary between 700 and 1000 • C, depending on reactor and feedstock [51]. Determination is difficult because, at higher temperatures, inorganic decomposition and gasification occur. ...
... Supplementary Materials: The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/ma15124130/s1. Supporting results and theory used for calculation are detailed in the Supplemental Material [16,26,34,51,109,121,. ...
Article
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Synthesizing biochar from mineral- and ash-rich waste biomass (MWB), a by-product of human activities in urban areas, can result in renewable and versatile multi-functional materials, which can also cater to the need of solid waste management. Hybridizing biochar with minerals, silicates, and metals is widely investigated to improve parent functionalities. MWB intrinsically possesses such foreign materials. The pyrolysis of such MWB is kinetically complex and requires detailed investigation. Using TGA-FTIR, this study investigates and compares the kinetics and decomposition mechanism during pyrolysis of three types of MWB: (i) mineral-rich banana peduncle (BP), (ii) ash-rich sewage sludge (SS), and (iii) mineral and ash-rich anaerobic digestate (AD). The results show that the pyrolysis of BP, SS, and AD is exothermic, catalyzed by its mineral content, with heat of pyrolysis 5480, 4066, and 1286 kJ/kg, respectively. The pyrolysis favors char formation kinetics mainly releasing CO2 and H2O. The secondary tar reactions initiate from ≈318 °C (BP), 481 °C (SS), and 376 °C (AD). Moreover, negative apparent activation energies are intrinsic to their kinetics after 313 °C (BP), 448 °C (SS), and 339 °C (AD). The results can support in tailoring and controlling sustainable biochar synthesis from slow pyrolysis of MWB.
... As previously shown (see Table 3), coconut fiber is a heterogeneous material constituted by different organic and inorganic components, as cellulose, hemicellulose, lignin, extractives, and ashes; presenting distinctive paths and mechanisms of pyrolysis that interfere with E a values. Increasing activation energy as a function of conversion is also related to the variation and amount of chemical constituents present in the raw material and their interactions [50,68]. Generally, the initial range of the lignocellulosic raw material thermal degradation is associated with the depolymerization of hemicelluloses, which has a low energy requirement. ...
... Generally, the initial range of the lignocellulosic raw material thermal degradation is associated with the depolymerization of hemicelluloses, which has a low energy requirement. On the other hand, cellulose presents more stable bonds, requiring more energy for breakage and degradation [68]. ...
Article
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This paper aims to investigate coconut fiber’s thermal behavior and evaluate its potential energy production through kinetic and thermodynamic studies, as well as the potential to produce solid biofuels (briquettes). Structural chemical analysis, proximate analysis, and higher heating value characterized coconut fiber. The thermogravimetric experiments were carried out in an inert atmosphere (N2), varying the heating rates at 5, 10, 15, and 20 K min⁻¹. The kinetic triplet was determined using isoconversional methods and master plot methodology. The pre-exponential factor, enthalpy, entropy, and Gibbs free energy parameters were calculated. The briquettes were made by different particle sizes: mixed particles (without granulometric classification); particles between 0.35 mm and 0.25 mm, and particles lower than 0.25 mm. The coconut fiber briquettes were produced in a compaction system at a temperature of 393.15 K under 15 MPa pressure for 20 min. This study also determined the apparent density, the resistance to diametral compression, and the energy density for coconut fiber briquettes. The pyrolysis reaction was modeled considering the reaction mechanism of as the three-dimensional Jader equation, with global activation energy 129.8 kJ mol⁻¹ and global pre-exponential factor 2.68 × 107 s⁻¹. The enthalpy and entropy values have shown considerable variations due to the conversion, suggesting that the pyrolysis of coconut fiber involves complex reaction mechanisms. The briquetting process enhanced the coconut fibers, and the results have shown that the lower particle size (particles ≤ 0.25 mm) presented better physical–mechanical properties and energy density. It is concluded that coconut fiber has the potential to be turned into biofuels from the thermochemical processes and may be enhanced by the densification process.
... Pyrolysis is a complex thermochemical process which cracks biomass into tar/bio-oil (liquid fraction), char (solid fraction), and non-condensable gases in different proportions depending on the biomass composition, operating conditions, reaction pathways, reactor design, etc. [50][51][52]. Though the process is primarily focussed on bio-oil production, the interest and research on employing different types of pyrolysis have been growing for charcoal and coke formation [53]. ...
... Though the process is primarily focussed on bio-oil production, the interest and research on employing different types of pyrolysis have been growing for charcoal and coke formation [53]. An extensive literature is available on different types of pyrolysis processes, as reported in Table A2 (Appendix B) with respect to chemistry, kinetics, reactors, and other practical aspects [34,52,54]. Bio-oil and biochar obtained from the pyrolysis process have attracted much interest because of their potential applications in diverse sectors. ...
Article
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This review article discusses the effects of inorganic content and mechanisms on raw biomass and char during gasification. The impacts of the inherent inorganics and externally added inorganic compounds are summarized based on a literature search from the most recent 40 years. The TGA and larger-scale studies involving K-, Ca-, and Si-related mechanisms are critically reviewed with the aim of understanding the reaction mechanisms and kinetics. Differences between the reaction pathways of inorganic matter, and subsequent effects on the reactivity during gasification, are discussed. The present results illustrate the complexity of ash transformation phenomena, which have a strong impact on the design of gasifiers as well as further operation and process control. The impregnation and mixing of catalytic compounds into raw biomass are emphasized as a potential solution to avoid reactivity-related operational challenges during steam and CO2 gasification. This review clearly identifies a gap in experimental knowledge at the micro and macro levels in the advanced modelling of inorganics transformation with respect to gasification reactivity.
... Numerous reviews can be found in the literature about the pyrolysis of single woody particles and its modelling. However, they mostly focus on the assessment of the accuracy of specific models and not on the general impact of the implemented model's components like directional dependency, relationships between parameters and kinetic schemes [7,8,[14][15][16][17][18][19][20][21][22][23]. ...
... Then, depending on the modelled temperature, the model has to be completed with the following reactions: thermal cracking of vapours, reactions between vapours and gases, steam gasification and Boudouard reaction. However, first, an assessment of the kinetic parameters for secondary cracking of volatiles has to be performed to indicate their appropriate value to be used in the single particle models [14,92]. ...
Article
Share link ( https://authors.elsevier.com/a/1f9lP4x7R2cZbB - free access till 19 July 2022) Thermochemical conversion of larger biomass particles (thermally thick regime) toward high-end products still suffers from an unrevealed quantitative relationship between process and product parameters. The main issue relates to the influence of heating rate within the particle, critical conversion-wise but difficult to assess experimentally. Computational fluid dynamics (CFD) modelling may help, but first the model must prove its reliability to prevent error transfer to the results. This study aimed to provide an unbiased, state-of-the-art model constructed in a stepwise mode to investigate the heating rate’s distribution. Several datasets with broadly varying parameters from the literature were used for the development and validation since the reproduction of datasets would not bring novelty to solving the problem. Instead of the model's calibration to fit to the data, the parameters for each step-model were meticulously selected to match the experimental conditions. The stepwise development showed the best accuracy when the anisotropy and the heat sink drying sub-model were implemented. Moreover, using the Ranzi-Anca-Couce (RAC) scheme led to more accurate results than the Ranzi scheme. The comprehensive model was positively validated against a broad range of production parameters (pyrolysis temperature: 500°C - 840 °C, diameter of particles: 10 mm - 20 mm, shapes: cylinders and spheres). Investigation showed a pattern in volatiles release profiles and homogeneous heating rate distribution when particle size is below 4 mm. Despite basing the models on the literature’s data, the study includes novel and valuable insights for biomass conversion and constitutes a solid foundation for future development.
... Other literature explains the kinetic parameters of biomass pyrolysis can also be modelled by volatile state approach under isothermal conditions [9,[34][35][36]. The process of biomass decomposition to volatiles has different mechanisms in response to each temperature increase at a constant heating rate [37][38][39]. This leads to the unique and different values of pre-exponential factor and activation energy under various decomposition treatments [40][41][42]. ...
Article
Background The determination of kinetic parameters of lignocellulosic biomass pyrolysis has been widely investigated through a solid-state approach using Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods. Unfortunately, the result of activation energy continues to escalate along with temperature and conversion which contradict the behavior of biomass pyrolysis kinetic. Hence, this study offers a new approach to overcoming those problems, namely volatile state approach. Methods The calculation was conducted by modifying solid-state KAS and FWO leading to volatile state KAS and FWO. The calculation for conversion in this approach starts from 0% and ends at not 100%. The data from Anca-Couce et al. were utilized and they were then plotted and calculated following volatile state KAS and FWO methods to acquire kinetic parameters. The difference in activation energy between the volatile state and solid-state was finally compared. Significant Findings Following the results, the activation energy obtained from volatile state KAS and FWO methods initially has an increasing value but then lessens as the pyrolysis temperature and conversion progress. This is in line with the involved activation energy should decrease at higher conversion. Therefore, the findings conclude that the volatile state approach contributes to revealing the nature of biomass pyrolysis with more logical and reasonable results.
... However, a further flowrate increase, up to 5L/min, decreased the bio-oil yield, showing an optimal operating condition. [217], [218]. The gas yield has similar behavior to the char yield. ...
Thesis
Microwave pyrolysis is a relatively new and exciting option for biomass residues treatment in terms of energy efficiency and high-quality products. During this thesis, two types of biomass, Sargassum, and Flax shives, were studied under microwave pyrolysis conditions. Preliminary studies were carried out to better understand the influence of temperature, moisture content, dielectric properties, biomass, and its pyrolysis products composition on the process. It was found that the thermochemical degradation of Sargassum occurs at a lower temperature in comparison to Flax shives; the increase in the moisture content increases the capability of biomass to convert microwaves into heat; and also, that Flax shives bio-oil and Sargassum bio-char were found to have interesting dielectric properties. The incident power, irradiation time, flow rate, and biomass load were the main factors considered to evaluate the effect of operating conditions on the microwave pyrolysis products. The liquid bio-oil samples and the non-condensable gas samples were recovered from each experiment and analyzed through gas chromatography-mass spectrometry (GC–MS) and gas chromatograph by flame ionization detection (GC-FID) to identify and quantify the different molecules present. The three phases of pyrolysis, dehydration, primary devolatilization, and passive lignin/residue degradation were identified during microwave irradiation. Bio-oil production was found to depend on two main parameters: the energy absorbed and the internal heating rate of the system. High heating rates of at least 120 °C/min and up to 200 °C/min provided the best bio-oil yields, and such rates can only be achieved by microwave technology by internal heating. The incident power, irradiation time, flow rate, and biomass load were the main factors considered to evaluate the effect of operating conditions on the microwave pyrolysis products. The liquid bio-oil samples and the non-condensable gas samples were recovered from each experiment and analyzed through gas chromatography-mass spectrometry (GC–MS) and gas chromatograph by flame ionization detection (GC-FID) to identify and quantify the different molecules present. The three phases of pyrolysis, dehydration, primary devolatilization, and passive lignin/residue degradation were identified during microwave irradiation. Bio-oil production was found to depend on two main parameters : the energy absorbed and the internal heating rate of the system. High heating rates of at least 120 °C/min and up to 200 °C/min provided the best bio-oil yields, and such rates can only be achieved by microwave technology by internal heating. Also, a scheme to scale up a microwave pyrolysis process is proposed. Various factors such as the cavity design, dielectric properties of the treated material, electromagnetic compatibility of the system, and biomass circulation are discussed, sorting the desirable conditions for continuously operated microwave reactors.
... An increased pyrolysis pressure improves the bio-oil decomposition inside the particles and concomitant increase final charcoal yield. However, the secondary char can exhibit different properties compared to classical charcoal, such as CO 2 reactivity or elemental composition [65,84,85]. One of the major disadvantageous of the bio-oil decomposition by primary pyrolysis is an increased oxygen content and lower carbon content of the charcoal [79], which can also result in an increased volatile matter content. ...
Article
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Renewable reductants are intended to significantly reduce CO2 emissions from ferro-alloy production, e.g., by up to 80% in 2050 in Norway. However, charcoals provide inferior properties compared to fossil fuel-based reductants, which can hamper large replacement ratios. Therefore, conditioning routes from coal beneficiation was investigated to improve the inferior properties of charcoal, such as mechanical strength, volatile matter, CO2 reactivity and mineral matter content. To evaluate the global warming potential of renewable reductants, the CO2 emissions of upgraded charcoal were estimated by using a simplified life cycle assessment, focusing on the additional emissions by the energy demand, required chemicals and mass loss for each process stage. The combination of ash removal, briquetting and high-temperature treatment can provide a renewable coke with superior properties compared to charcoal, but concomitantly decrease the available biomass potential by up to 40%, increasing the CO2-based global warming potential of industrial produced charcoal to ≈500 kg CO2-eq. t−1 FC. Based on our assumptions, CO2 emissions from fossil fuel-based reductants can be reduced by up to 85%. A key to minimizing energy or material losses is to combine the pyrolysis and post-treatment processes of renewable reductants to upgrade industrial charcoal on-site at the metallurgical plant. Briquetting showed the largest additional global warming potential from the investigated process routes, whereas the high temperature treatment requires a renewable energy source to be sustainable.
... As can be seen from the table that the pre-exponential factor values for all the runs are in the range of 7.54 × 10 4 -8.62 × 10 6 (s −1 ). This low range of (< 10 9 s −1 ) pre-exponential factor values indicates that the pyrolysis of the food wastes could be a surface reaction or closed complex reaction [58]. The activation energy values for the samples were between 15 and 26 kJ/mol. ...
Article
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The amount of food waste that is generated all over the world is enormous. As food wastes are rich in nutrients and organics, they serve as a potential source for the generation of many value-added commodities and energy. In most countries, food wastes are predominately dumped in open lands or incinerated, along with other combustible materials such as municipal solid wastes, for the possible extraction of energy. However, these two modes of food wastes disposal are encountering more and more environmental, technical, and economical challenges. More recently, it has been realized that food wastes can be transformed into energy and value-added products, such as horticultural biochars, using thermochemical technologies such as pyrolysis and gasification. In the current research work, three selected food items, carrots, cucumbers, and tomatoes, have been studied using thermogravimetric analysis. The biochar analysis involves one single food item (carrot), one binary mixture (carrot + cucumber), and one ternary blend of carrot, cucumber, and tomato. Two heating rates were used in order to perform kinetic modeling studies using the Arrhenius and Coats-Redfern models. Since the production of the pyrolysis gases—for energy and chemicals production—is of major economic significance regarding the overall process viability, the TGA syngas for a single component, binary component and tertiary component systems were analyzed by TGA coupled mass spectrometry. The results of the gas analysis indicate an increase in hydrogen generation due to blending the food wastes.
... From DTG findings (Fig. 1 B) and a table presented in ESI, the first peak was observed at 80 • C temperature due to the removal of moisture content from DR biomass. Additionally, the peaks were noticed at 250-340 • C, and 323-383 • C indicated hemicellulose, and cellulose decayed within the temperature ranges of 250-290 • C and 323-346 • C at 5 • C min − 1 ; 258-300 • C and 335-356 • C at 10 • C min − 1 ; 266-310 • C and 347-367 • C at 20 • C min − 1 ; 276-326 • C and 360-375 • C at 35 • C min − 1 ; 286-340 • C and 365-383 • C at 55 • C min − 1 respectively (Di Blasi, 2008). Finally, no sharp peaks were observed at (>550 • C) temperature for the lignin decomposition stage. ...
Article
The aim of this work was to study the pyrolysis of Delonix regia biomass with non-isothermal thermogravimetric experiments. The targeted objective was to investigate kinetic triplets and thermodynamic parameters. Five iso-conversional methods, namely Differential Friedman, Kissinger-Akahira-Sunose, Ozawa-Flynn-Wall, Starink, and Distributed Activation Energy, have been considered. In the adopted heating rates of 5-55 °C min-1, the average activation energy and pre-exponential factor varied in the range 202.34 - 205.89 kJ mol-1 and 4.98 × 1017 - 2.04 × 1020 s-1 respectively. Corresponding average enthalpy and Gibbs free energy varied from 196.84 to 200.87 kJ mol-1 and from 182.64 to 206.41 kJ mol-1 respectively. Pyrolysis mechanism have been confirmed by Avrami-Erofeyev (A4), power-law (P2 and P4) and reaction (F1, F2, and ≥F5) according to Criado's master plots.
... Design and optimization of pyrolysis reactors can be done effectively with the help of fundamental decomposition studies. More accurate models are needed for multi-component mixtures in fluidized bed pyrolysis reactors (Di Blasi, 2008). The coupled particle and reactor scale simulations are essential to understand the biomass fast pyrolysis reactors. ...
Article
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Pyrolysis is one of the thermochemical conversion platforms for biomass and plastics into value-added product resources. The products formation significantly varied with feedstock composition, pyrolysis parameters, and heating source. Hence, the objectives of this review article are to understand the role of type of feedstock, heating rate, reaction temperature, residence time, feedstock particle size, and type of pyrolysis reactor. In addition, the upgradation of bio-oil using physical and catalytic approaches has been analyzed. Co-pyrolysis and catalytic co-pyrolysis which promote the product properties through synergy are also investigated. The role of microwave heating with the help of a susceptor to promote product synthesis is discussed. The metal oxide and zeolite catalysts' role in the formation mechanism of hydrocarbons and oxygenates are studied. For the future scope, the studies related to pyrolysis-combustion combination, microwave hybrid heating, and continuous catalytic co-pyrolysis are promising approaches. To this end, this review bridges the research gap in the domain of pyrolysis process parameters, and waste valorization using microwave-assisted pyrolysis, co-pyrolysis, and catalytic co-pyrolysis technologies. Moreover, this review would further provide the way for the current issues related to effective biomass and plastic waste utilization.
... They include the motion of the pieces of biomass (from here on referred to as particles) their heating-up, drying, shrinkage and the primary pyrolysis involving a very large number of chemical reactions. It is therefore complex to investigate [1]- [6] and the detailed modeling often requires the use of supercomputers [7]- [10]. One parameter of major importance for this process is the heat transferred to the packed bed of solid particles by conduction, convection and radiation. ...
Conference Paper
This work presents the further development and the validation of the Discrete Ordinates Model for thermal radiation which is implemented in OpenFOAM ® for application to packed beds of biomass particles. This radiation model is an important part of a more comprehensive model which simulates the thermal conversion of discrete phase (here for instance wet biomass particles) which flows continuously inside an indirectly heated rotary kiln. The comprehensive Eulerian-Lagrangian model integrates three-dimensional, time-resolved simulation of the essential chemical and physical processes occurring within and in-between the moving bed of particles. This is realized by combining the particle collision models for non-reactive dense flows with models for heat transport, phase change and chemical reaction for multiphase reacting flow in the framework of OpenFOAM ®. For the thermal treatment of solid particles, convection and radiation heat transfer methods couple the energy exchange between the reactor wall, gas-and disperse phase. The original implementation of the finite volume Discrete Ordinate Model (fvDOM) valid for a dilute particulate phase neglects the effect of local opacity due to the existence of individual particles. However, in the present application, a dense-packed bed of the particulate phase exists in the reactor. Therefore, in this study, this direction-based radiation model is adjusted for a computational cell with arbitrary particle volume fractions. To validate the results with the present thermal radiation model, first a simple test case with heating the bed of particles from the top of the domain is carried out. A second test relates to a laboratory-scale reactor. The results of the improved fvDOM are compared to the original implementation of OpenFOAM ® and the more simple and computationally cheap P-1 radiation model. In general, the P-1 model largely overpredicts the radiative heat transfer while the original fvDOM underpredicts the heat flux by about 15% for the first test case. The improved model delivers results within 1% deviation at the expense of maximum 10% of the increase in the computational time.
... At the same time, lignin decay occurred at a slower rate (but at >500 • C) with no sharper peaks. Di Blasi (2008) stated that HC, CEL, and LIG decayed at 225-325 • C, 325-375 • C, and 417-607 • C, respectively. Furthermore, peaks observed at 460-546 • C represents the detection of isobutylene with the temperature range of 460-492, 465-511, 484-533, 495-542, and 501-546 • C at 5, 10, 20, 35, and 55 • C min − 1 heating rates. ...
Article
Non-isothermal co-pyrolysis of Delonix regia and tube waste was carried out using a thermogravimetric analyzer under nitrogen atmosphere at temperatures 25 to 1000 °C, with heating rates between 5 and 55 °C min⁻¹. The kinetic triplets were estimated using five iso-conversional models: Differential Friedman, Kissinger-Akahira-Sunose, Ozawa-Flynn-Wall, Starink, and Distributed Activation Energy Method. In kinetic analysis, the average activation energy (Eα, kJ mol⁻¹) and frequency factor (ko, min⁻¹) values were 230.47 and 2.55× 10³⁰; 208.13 and 8.31× 10²⁶; 207.78 and 1.58× 10²⁴; 208.38 and 6.47× 10²⁶; 208.13 and 5.15× 10²⁶; respectively. In thermodynamic analysis, average values of ΔH, (kJ mol⁻¹), and ΔG, (kJ mol⁻¹) were 225.38, 179.9; 225.28, 180.22; 225.18, 180.31; 225.08, 180.99; and 224.98, 182.15; respectively. Criado's master plot revealed a multistep reaction mechanism for the co-feed.
... Due to the overlapping peaks, DTG deconvolution method was applied. This method has been already used in a wide variety of biomass studied (Diblasi, 2008;Sronsri and Boonchom, 2017) and it perfectly allows the separation between peaks, being possible the obtention of each peak area. This area value is related to the percentage of the corresponding compound in lignocellulosic biomass, thus the full fiber analysis can be obtained considering the total amount of volatile matter (Equation 2). ...
Article
Almonds are considered one of the most valuable fruits worldwide due to its high nutritional value. Moreover, a growing attention has been paid over the last years to other parts of the fruit, such as skins, shells or hulls, which are commonly found as almond by-products and scarcely exploited for valorization. In this study, two approaches were evaluated. Firstly, a green innovative processing technology, pulsed electric fields (PEF), was applied for the first time to assist the extraction of antioxidant compounds from almond hull biomass (AH). In particular, this technology was used with the aim of developing a feasible valorization strategy, being a sustainable alternative for polyphenols extraction compared to traditional methods. Then, the total phenolic content (TPC) and the antioxidant activity (TEAC and ORAC values) were measured, obtaining a higher extraction of TPC and TEAC values when PEF was used compared to conventional soaking. Secondly, the characterization of AH by means of fiber, ultimate and proximate analysis was carried out. Ultimate and proximate analysis provided information about the exploitation towards bioenergy and biofuels, demonstrating the so-called derived AH-EFB being useful for that purpose. Moreover, the high percentage in terms of carbohydrates suggests that AH could be a useful source for high-added-value chemicals, such as levulinic acid, furfural and 5-hidroximethylfurfural, displaying an interesting energetic valorization route for this biomass.
... In biomass conversion, the combustion of volatile gases represents about 70 %− 80 % of the energy release (Sami et al., 2001). Although the composition of the volatile gases is quite diverse and depends on various factors such as particle temperature, heating rate, residence time or particle size (Lu et al., 2008;Yin et al., 2010), many authors concur that permanent gas composition of volatiles includes CO, CO 2 , CH 4 and H 2 (Jiang et al., 2018;Sami et al., 2001;Di Blasi, 2008;Neves et al., 2011;Ku et al., 2014). ...
Article
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Determination of the explosion severity parameters of biomass is crucial for the safety management and dust explosion risk assessment of biomass-processing industries. These are commonly determined following experimental tests in the 20L sphere according to the international standards. Recently, CFD simulations have emerged as a reliable alternative to predict the explosion behavior with good accuracy and reduced labor and capital. In this work, numerical simulations of biomass dust explosions are conducted with the open-source CFD code OpenFOAM. The multi-phase (gas-solid) flow is treated in an Eulerian-Lagrangian framework, using a two-way coupling regime and considering the reactions of biomass conversion (moisture evaporation, devolatilization, and char oxidation), the combustion of volatile gases, and convective and radiative heat transfer. The model is validated with pressure-time and concentration-dependent experimental measurements of two biomass samples. Results suggest that the characteristics of the cold-flow (ı.e. turbulence levels, actual dust concentration, spatial distribution of the dust cloud, and turbophoresis effect) govern the course of the explosion process, and depend strongly on particle size, dust concentration, and ignition delay time effects. These findings may be relevant in the design of better dust explosion testing devices and to the reexamination of the guidelines for the operation of the experiment. Finally, a thorough discussion on the explosion pressures, degree of biomass conversion, flame temperature, flame propagation patterns, and the dust agglomeration effect is presented.
... However, the level of decomposition is dependent on wood species, heating conditions and accessibility of oxygen to the sample surface [23]. It was observed in Di Blasi's study [48] on wood decomposition that samples with high lignin levels showed higher mass loss rates in the second stage. Mass loss of wood samples in the thermal oxidative decomposition process occurs at lower temperatures than in a nitrogen atmosphere. ...
Article
Wood is undeniably the most useful and readily available natural raw material. However, the susceptibility of wood products to fire is one of the crucial challenges faced in the wood industry. The fire behaviour of wood is a very complex phenomenon due to the different constituents and their independent reactions to fire. This article presents a thorough overview of the flammability stages of wood. It covers pyrolysis, thermal oxidative decomposition, ignition, combustion and heat release as well as flame extinction mechanisms. In the area of flame retardancy, conventional wood fire retardants, nanocomposites fire retardants and wood modification processes are investigated. Factors such as wood species, moisture content, density, experimental conditions such as external heat flux, heat exposure time, wood permeability and porosity are some of the deterministic parameters characterising the fire behaviour. This paper is a one-stop-shop for researchers analysing wood flammability due to the inclusion of all aspects pertaining to the burning of wood.
... In biomass conversion, the combustion of volatile gases represents about 70%-80% of the energy release [80]. Although the composition of the volatile gases is quite diverse and depends on various factors such as particle temperature, heating rate, residence time or particle size [81,82], many authors concur that permanent gas composition of volatiles includes CO, CO 2 , CH 4 and H 2 [35,58,80,[83][84][85]. ...
Preprint
Determination of the explosion severity parameters of biomass is crucial for the safety management and dust explosion risk assessment of biomass-processing industries. These are commonly determined following experimental tests in the 20L sphere according to the international standards. Recently, CFD simulations have emerged as a reliable alternative to predict the explosion behavior with good accuracy and reduced labor and capital. In this work, numerical simulations of biomass dust explosions are conducted with the open-source CFD code OpenFOAM. The multi-phase (gas-solid) flow is treated in an Eulerian-Lagrangian framework, using a two-way coupling regime and considering the reactions of biomass conversion (moisture evaporation, devolatilization, and char oxidation), the combustion of volatile gases, and convective and radiative heat transfer. The model is validated with pressure-time and concentration-dependent experimental measurements of two biomass samples. Results suggest that the characteristics of the cold-flow (\i.e. turbulence levels, actual dust concentration, spatial distribution of the dust cloud, and turbophoresis effect) govern the course of the explosion process, and depend strongly on particle size, dust concentration, and ignition delay time effects. These findings may be relevant in the design of better dust explosion testing devices and to the reexamination of the guidelines for the operation of the experiment. Finally, a thorough discussion on the explosion pressures, degree of biomass conversion, flame temperature, flame propagation patterns, and the dust agglomeration effect is presented.
... According to Di Blasi [17], the reaction orders of multi-component devolatilization reactions range between 0.8 and 1.8, depending on the biomass. Moreover, Albis et al. [18] found that reaction order during pyrolysis of pure hemicellulose is 2, but they revealed that adding a catalyst could increase or decrease it. ...
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A new approach is proposed to obtain the kinetic parameters of biomass pyrolysis mixed with calcium catalyst. This approach involves the optimization of least squares (LS) with the Coats-Redfern integral method to avoid mathematical biases that may appear when applying the linear regression approach. The method was applied to the TGA data of pyrolysis of corn cob and corn cob mixed with 20 or 40 % by weight of CaO or CaCO3 under N2 atmosphere at temperatures between 25 and 700 °C. For raw cob, r² reaches 0.997. For corn cob mixed with 20 % by weight of CaO or CaCO3, r² reached 0.996 − 0.998, and for 40 % by weight, r² reached 0.836 − 0.957. Applying this method, the activation energy (EA) value of the raw cob pyrolysis is 58.35 kJ mol⁻¹, while the addition of CaO or CaCO3 increases the EA to 69.33 and 66.07 kJ mol⁻¹, respectively. The method is simple to use and allows reliable values of kinetic parameters.
... When using kinetic models, the question of the number of reactions and their sequence is considered. The modeling of processes using various approaches is discussed in [40]. A one-component mechanism of primary pyrolysis assumes that gas, tar and char are formed from the biomass with different reaction rates. ...
Article
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In order to predict and assess the danger from crown forest fires, it is necessary to study the thermal degradation of different forest fuels in a high-temperature environment. In this paper, the main characteristics of pyrolysis accompanied by moisture evaporation in a foliage sample of angiosperms (birch) were investigated within conditions typical for a crown forest fire. The heat and mass transfer in the forest fuel element is described by the system of non-stationary non-linear heat conduction equations with corresponding initial and boundary conditions. The considered problem is solved within the framework of the three-dimensional statement by the finite difference method. The locally one-dimensional method was used to solve three-dimensional equations for heat conduction. The simple iteration method was applied to solve nonlinear effects caused by the forest fuel pyrolysis and moisture evaporation. The fourth kind of boundary conditions are applicable at the interface between the sub-areas. Software implementation of the mathematical model is performed in the high-level programming language Delphi in the RAD Studio software. The characteristic changes in the sample temperature field and the phase composition under high-temperature exposure from a forest fire are presented. The induction period of the thermal decomposition of dry organic matter in the sample was determined. Recommendations are made about key features of accounting for the pyrolysis and evaporation processes when predicting forest fire danger. The research results can be used in the development and improvement of systems for predicting forest fire danger and environmental consequences of the forest fires.
... As a result of the rising rate of modern structures that use timber-based products in furniture and construction structure applications [1], the prediction of burning rate, ignition, smoke, and pyrolysis is a crucial point. Pyrolysis is an endothermic process, a thermal degradation that occurs without the need of an oxidizer as a result of heat exposure [2][3][4][5][6]. Because of its limited thermal conductivity and high specific heat, pyrolysis of lumber occurs in three stages: moisture transfer below 200 • C, commencement of pyrolysis up to 300 • C, and fast pyrolysis over 300 • C. Furthermore, in order to measure pyrolysis, flammable materials must be burned and extinguished [7]. ...
Article
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This paper anticipates the burning rate and optical obscuration characteristics of a 10 mm thick timber species often used in buildings under the influence of a guided flame condition with heat fluxes of 25 kW/m² and 50 kW/m². The smoke density chamber was used to test the wood species Pinus strobus, Pinus kesiya, Quercus alba, and Faqus sylvatica. The experimental data: time, specific gravity, mass loss, and heat flow were used as input variables to an artificial neural network (ANN) model. ANN with structure of 4-64-32-2 was built and validated, the results revealed that, the correctness of the established simulation was proven by a high value of R² (0.99292 for validation) and highest validation performance (MSE = 17.809 at epoch 12). When the heat flow was reduced from 50 kW/m² to 25 kW/m², Quercus had the greatest drop in mass optical density (MOD). In the case of 25 kW/m², the average charring rate was roughly 0.57 mm/min, compared to 0.96 mm/min in the case of 50 kW/m². The MOD declines asymptotically for all species regardless of heat flux. The findings give statistical support and theoretical reference for fire-related construction norms and standards.
... Reduced-order models are thus required to render the pyrolysis process computationally tractable. Attempts to capture the complexity of the pyrolysis mechanism with significantly simpler kinetics have included single-component/single-step, single-component/multi-step, multi-component/single-step, and multi-component/multi-step kinetics (Di Blasi, 2008). Ranzi et al. (2008) published a gas-phase chemical mechanism that relied on species that are produced in their multi-component/multistep pyrolysis kinetic model. ...
Article
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Computational simulations have the potential to provide low-cost, low-risk insights into wildland fire structure and dynamics. Simulation accuracy is limited, however, by the difficulty of modeling physical processes that span a wide range of spatial scales. These processes include heat transfer via radiation and turbulent advection, as well as both solid- and gas-phase chemistry. In the present study, we perform large eddy simulation (LES) with adaptive mesh refinement to model the multi-phase pyrolysis and combustion of dry Douglas fir, where temperature-based lookup tables corresponding to a multi-step pyrolysis mechanism are used to represent the composition of gas-phase pyrolysis products. Gas-phase and surface temperatures, mass loss, and water vapor mole fraction from the LES are shown to compare favorably with experimental measurements of a radiatively heated Douglas fir fuel sample undergoing pyrolysis and combustion beneath a cone calorimeter. Using frequency comb laser diagnostics, optical and infrared cameras, and a load cell, the experiments provide simultaneous in situ , time-resolved measurements of chemical composition, temperature, and mass loss. The present study thus combines cutting edge computational and experimental techniques with multi-step chemical pyrolysis modeling to provide a validated computational tool for the prediction of solid fuel pyrolysis and combustion relevant to wildland fires.
... Pyrolysis will yield mainly biochar at low temperatures, less than 450 o C, when the heating rate is quite slow, and mainly gases at high temperatures, greater than 800 o C, with rapid heating rates. At an intermediate temperature and under reliably high heating rates, the main product is bio-oil [10] . ...
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This article is based on the alternate solution of different global problems and the solutions relat ed to solid waste management. The renewable fuels were produced by the pyrolysis of buffalo dung. After the removal of moisture content by drying under sunlight the pyrolytic process of dry buffalo dung was carried out in the self-designed pyrolytic reactor. The heat was supplied by natural gas combustion for four hours that resulted in the highly flammable synthetic gas, liquid fuels and biochar. The flame test and TLC examination of the liquid fuels showed that the fuels so obtained are aromatic in nature. The biochar so obtained from the pyrolysis of buffalo dung was used as biofertilizer by using the okra seeds as test experiment. The biochar showed the greater potential as a biofertilizer as compare to normal buffalo dung. Biowastes pyrolysis has been attracted much attention due to its high efficiency and availability across the globe. It also provides an opportunity for the management of municipal solid wastes into clean energy. The production of fuels from sustainable sources like pyrolysis of buffalo dung will reduce the fuel crisis and environmental pollution. In addition, this article will provide the mechanism for the management of solid waste by promoting the waste-to-zero waste technology through the production of useful products.
Article
In this work, a novel method for extraction of manganese from low-grade pyrolusite by a sawdust pyrolysis reduction roasting-acid leaching process was explored. The reduction roasting was studied systematically, and the mechanism was also explored by thermodynamic and phase change analysis. Results indicate that sawdust was rapidly pyrolyzed at 250–450°C to generate a large amount of reducing gases such as CO, CH4, and H2, which gradually reduced MnO2 in low-grade pyrolusite to MnO. The reduction process of MnO2 was identified as MnO2→Mn2O3→Mn3O4→MnO. It was proved that MnO2 of low-grade pyrolusite could be reduced effectively to MnO at lower temperature and shorter duration time by sawdust pyrolysis. Meanwhile, the optimum leaching efficiency of 99.45% for manganese could be attained when sawdust dosage was 11% of the mass of low-grade pyrolusite, the roasting temperature was 500°C, and the roasting time was 25 min.
Article
By extending the bonded particle method, the major structural changes during the devolatilization of a wood pellet in a fluidized bed and the resulting mechanical behavior have been successfully reproduced. A comparison with experiments from the literature showed that the implemented particle-based pyrolysis model enables predicting the entire pellet’s kinetics with a high agreement. The developed shrinkage model for the particles and bonds further allowed to emulate the reported formation of a large-scale pore network inside the pellet. The simulation of a radial compression test with the predicted structure showed good agreement with experimental data and could confirm the importance of the pores for the mechanical behavior. The results demonstrated that the large pores cause the fragmentation of agglomerates already at low mechanical loads which could promote attrition. In general, the results have shown that the developed extension of the bonded particle method allows studying and predicting the behavior of a single pellet during conversion inside a fluidized bed gasification reactor in more detail.
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To investigate the differences in the pyrolysis characteristics of leaves of sweet cherry tree ( Prunus avium L.) under rain-shelter cultivation (RS) or under open-field cultivation (CK), thermogravimetric (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) curves were compared at three heating rates of 10, 20 and 30°C·min − 1 . There were two obvious mass loss peaks at 280°C and 330°C, which were manifested by the slow pyrolysis of hemicellulose in the low temperature region and the rapid pyrolysis of cellulose in the high temperature region, respectively. The curve in the pyrolysis range after 440°C was stable, and the mass change corresponded to the pyrolysis of a small amount of macromolecular organic extracts and inorganic salts. When the temperature reached 600°C, approximately 69% and 73% of the CK and RS leaves were thermally destroyed, respectively. The Coats-Redfern method was used for kinetic calculations to obtain an activation energy of 29.75 ~ 36.14 kJ·mol − 1 in the first-order pyrolysis kinetics stage. The second-order pyrolysis kinetics stage can fit the pyrolysis process well. The pyrolysis characteristics and kinetic parameters of the leaves were related to the heating rate and the hemicellulose content, cellulose content and lignin ratio in each sample.
Article
Syngas production from biomass resources suggest considerable privileges to attain energy sustainability in future. Design and control strategies are essential to extend the technology of biomass gasifiers, which require reliable model developments. The overarching contribution of this study is to develop and evaluate a three-stage biomass gasifier model. The model consists of three successive sub-models for drying and pyrolysis, partial oxidation and char reduction reactors. The pyrolysis of raw material is simulated based on the ligno-cellulosic structure of the biomass by adopting comprehensive kinetic rate modelling approach. The partial oxidation sub-model is built by axis-symmetric 2D transport equations including detailed chemical scheme. Char reduction sub-model is extended based on axis-symmetric 2D DPM model accompanied by appropriate chemical kinetic scheme considering heterogeneous and homogeneous reactions. Accuracy of each sub-model is separately verified by comparison with available numerical and experimental data. Moreover, the correctness and predictability of the complete gasifier model is evaluated using two experimental reports. For both cases, investigations demonstrate high resolution agreement between the results of the developed model and available experimental measurements both thermally and chemically. Furthermore, a parametric analysis is conducted to investigate the gasifier performance against the variations of the main system operating parameters including the type of the feeding biomass and its moisture content, equivalence ratio and air initial temperature. Based on the results, higher volatiles mass fractions and lower char mass fraction have been produced from pyrolyzing of hardwood in comparison with beech wood. Also, Results reveal that with increase of the moisture content from 15% to 35%, syngas LHV and cold gas efficiency reduce by 1.9559 MJ. kg⁻¹ and 25.78% respectively, while H2 mole fraction at the gasifier outlet rises by 0.90%. On the contrary, growth of equivalence ratio from 2 to 10 leads to the drastic increase of syngas LHV by 5.6404 MJ. kg⁻¹, however, cold gas efficiency peaks to 82.75% at the equivalence ratio of 4. Besides, varying the inlet air temperature over a range of 500 K–1300 K causes 0.6938 MJ. kg⁻¹ growth of syngas LHV as well as 9.43% rise of cold gas efficiency.
Article
This study paves a strategy to better understand the thermal conversion of biomass residues. In particular, a comprehensive study to determine the multi-step reaction model to describe the pyrolysis process of brewer's spent grain from Pilsner (PBSG) and Weizen (WBSG) malts, and beech wood chips (BWC) has been presented. The results of the kinetic triplet optimisation show that the process begins with a nth order reaction Fn (n = 1.74, 1.52, 1.54) for extractives, followed by Avrami-Erofeev type nucleation reactions An (n = 1.50, 1.50) for hemicellulose, with the exception of beech hemicellulose that follows the nth order mechanism Fn (n = 1.25), and An (n = 1.50, 1.50, 1.50) for cellulose, for PBSG, WBSG and BWC, respectively. Moreover, by virtue of the comprehensive approach proposed in this study, a single nth order mechanism Fn with n = 1.19, 1.23, 1.32 for PBSG, WBSG and BWC, respectively, has been obtained for the lignin. The developed model have been used to support the design of a pilot-scale down-draft gasifier for the thermal valorisation of brewer's spent grain.
Chapter
Bioenergy is a widespread form of modern renewable energy source because of the devastating impacts of high demand for fossil fuel, i.e., global warming and environmental effects. This paper addresses the different engineering aspects of bioenergy and its international status. Bioenergy deals with their chemical structure, characterization, technologies available for conversion, scientific processes and their related products, all of which are are reviewed and discussed. Moreover, bioenergy‐derived products are analyzed from environmental and techno‐economic considerations, and observations and remarks are presented. Finally, the challenges faced expand the share of bioenergy employments in the global energy market and developed countries.
Article
Composition of pyrolysis gases for wildland fuels is often determined using ground samples heated in non-oxidising environments. Results are applied to wildland fires where fuels change spatially and temporally, resulting in variable fire behaviour with variable heating. Though historically used, applicability of traditional pyrolysis results to the wildland fire setting is unknown. Pyrolytic and flaming combustion gases measured in wind tunnel fires and prescribed burns were compared using compositional data techniques. CO2 was dominant in both. Other dominant gases included CO, H2 and CH4. Relative amounts of CO, CO2 and CH4 were similar between fire phases (pyrolysis, flaming combustion); relatively more H2 was observed in pyrolysis samples. All gas log-ratios with CO2 in pyrolysis samples were larger than in flaming combustion samples. Presence of live plants significantly affected gas composition. A logistic regression model correctly classified 76% of the wind tunnel samples as pyrolysis or flaming combustion based on gas composition. The model predicted 60% of the field samples originated from pyrolysis. Fire location (wind tunnel, field) and fire phase affected gas composition. The compositional approach enabled analysis and modelling of gas compositions, producing results consistent with the basic characteristics of the data.
Article
An in-depth investigation of the chemical structural evolution of char throughout the pyrolysis process is critical for subsequent biochar utilization. Therefore, the interaction mechanism among biomass constituents was studied by the examination of product distribution, bio-oil and bio-gas composition, organic functional groups, and two-dimensional correlation infrared spectrum characteristic of char. Char evolution was influenced by primary interaction (at 300 or 400 °C) and secondary interaction (at 500 or 650 °C). Polymer depolymerization and phenylpropane side chain breaking were aided by the primary interaction. Due to a “melting and wrapping” effect, it hindered ring opening, recombination, and polymerization of D-allose/D-xylose molecules, allowing the char to preserve its original C-O-C and C-OH structure. The secondary interaction stimulated the cyclization and intramolecular dehydration of D-allose, leading pyrolysis to advance to the pyran pathway. It also encouraged the ring opening, cyclization, rearrangement, and polymerization of monomer molecules, resulting in the char's C = O, C = C, and C-OH structures with greater aromatization degree. The discovery advances the understanding of the interacting mechanism of biomass pyrolysis and char formation.
Article
The upswing of argan’s oil for the cosmetic industry has increased the farming of this plant and originated an unexplored residue of complex treatment, its nutshells. This work deals with the characterization of this feedstock, its pretreatment via torrefaction and its gasification either with or without the pretreatment stage. Torrefaction was carried out in a continuous auger reactor at two temperatures, 220 and 250 °C. Hemicellulose was almost totally removed from argan nutshells after torrefaction. Compared to the raw argan shells, the torrefied solids showed an increased content of fixed carbon, a noticeable reduction in the O/C ratio and a significant increase in the HHV, the higher the torrefaction temperature. Chemical thermodynamic equilibrium calculations were implemented to the gasification stage to calculate the equivalence ratio for auto-thermal operation and to assess the effect of temperature and steam-to-biomass ratio on gas yield and composition. Air-steam gasification was also experimentally tested for the raw and torrefied materials at the operational conditions drawn from the simulation results. The torrefied material gasification yielded four times more char than the raw material, while tar production from the torrefied material was only reduced in the presence of steam (anyway starting from a low value: 0.7 g/m³STP for raw argan shells vs 0.3 g/m³STP for the torrefied material). Nor gas production, neither the H2/CO ratio nor the energy content in syngas were improved by gasifying the torrefied material, so torrefaction does not appear to be a profitable pretreatment stage for the gasification of argan nutshells from the point of view of syngas quality.
Article
A hybrid optimization algorithm, combining both Particle Swarm Optimization (PSO) and Genetic Algorithm (GA), is proposed to gain the favorable features of each individual algorithm when determining the pyrolysis kinetics of biomass. High convergence efficiency and the capability of avoiding being trapped in local optimal solution are primarily associated with PSO and GA, respectively. Gene operations in GA, including selection, crossover and mutation, are partially incorporated into PSO to increase the population diversity. Pyrolysis of beech wood was experimentally studied at three heating rates, and a numerical solver was established to simulate the pyrolysis details. In order to demonstrate the improved performance of PSO-GA, two pyrolysis models with given reaction schemes and kinetic parameters were adopted to create the acritical thermogravimetric analysis (TGA) curves. Then the kinetics was estimated using PSO-GA and individual GA and PSO. Subsequently, the experimental data were analyzed with the same manner. The results show that PSO-GA has the highest possibility of obtaining desired outcomes followed by PSO and then GA. With fixed population size, PSO-GA converges to a lower fitness function value, corresponding to higher accuracy. The attained kinetics of wood falls into the reported ranges in the literature. In some scenarios, the optimized results of hemicellulose and lignin contradict with the existing conclusions even though the global curves match the experimental measurements well. This implies the general concept of the pyrolysis process should also be given adequate consideration to avoid potential compensation effect when encountering complex issues.
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The final composition of volatile components in the process of oxidative pyrolysis depends on the temperature level of the process. The gas output increases with the growth of hydrogen, methane and heavy hydrocarbons concentration in the process of pyrolysis in the range of 200-500°C. In this case, there is a noticeable decrease in undesirable impurities in the output of carbon dioxide and nitrogen in the fuel gas. The obtained data on the dynamics of thermal decomposition of biomass under heating conditions reflect the complex dependence of the yield of total gas individual components both on time and on the temperature of the process. The more volatiles contained in the source fuel, (the other things being equal) the faster the gas mixture ignites, and the more intensely it burns out. The composition and temperature of the gas mixture affects the pressure drop and auto-ignition temperature in the pyrolysis chamber. It was found that the lowest self-ignition temperature of a gas mixture is 490°C. A series of experiments to determine the critical condition for self-ignition at a constant temperature of 490°C and various initial pressures of the mixture (100-300 kPa) was carried out. It was found that the transition from a smooth increase in pressure of 90 kPa to an explosive one (up to 300-400 kPa) depends on the composition and temperature of the gas mixture. Therefore, the composition of the gas and its ignition temperature can be controlled by adjusting the mode of pressure increase in the reactor.
Article
This paper is focused on aerosol fine particle release during the thermal decomposition of beech wood samples with identical mass under an oxidizing and inert atmosphere. This thermal degradation of wood is a significant part of the biomass combustion and pyrolytic process. This contribution focuses on nanoparticles emission with specifying sizes and concentrations in the range of 18–545 nm during thermal degradation processes and determining correlations between individual thermal degradation processes of a wood sample with the same weights but with different heating rates. The flue gases' chemical composition was simultaneously analyzed using a quadrupole mass spectrometer during the thermal degradation process. The weight loss of the sample and its derivation were monitored using a thermogravimeter. This combination made it possible to identify the ranges with the highest particle emission concerning the wood sample and the sample's heating rate. The fine particle identification apparatus uses a Scanning Mobility Particle Sizer and a condensation particle counter. This experimentally obtained data were then compared with the numerical model CPD-Bio. In this case, the comparison was focused on the prediction of the temperatures of the individual pyrolysis stages, at which gaseous products and especially tars are formed.
Article
The unsustainable management of sewage sludge induces environmental and economic issues, yet sewage sludge is a promising feedstock for the production of biofuels by pyrolysis. Actual challenges include poor chemical stability, high water content, high viscosity, high concentrations of nitrogen, and the presence of oxygen in the produced biofuels. Moreover, the produced biochars contain elevated amounts of toxic metals and, as a consequence, may not be used in agricultural soils. Here we review the co-pyrolysis of sewage sludge with other materials to enhance bio-oil quality. Several studies show that co-pyrolysis of sewage sludge with non-biomass materials reduces water, oxygen and nitrogen contents, activation energy, and enthalpy; and increases the calorific value.
Article
Hydrogen release during pyrolysis of woody biomass is studied considering anisotropicity and inhomogeneity of wood structure. A new anisotropic shrinkage model is proposed based on the decomposition of main wood constituents, i.e., cellulose, hemicellulose, and lignin. The new shrinkage model can predict the temporal evolution of the wood structure, and the differences between axial and radial shrinkage during pyrolysis. The model agrees very well with several experimental data from the literature. Based on particle temperature during conversion, the pyrolysis is partitioned into four stages, and the hydrogen release and H2 formation from each stage are investigated. Stage (IV) of pyrolysis, from 1000 to 1273 K, is found to be efficient for H2 production owing to the production of considerable mass of H2 with a minimal amount of tar species. Furthermore, the char quality is found to be different at the end of stages (II), (III), and (IV), where around 67.7, 80.5, and 93.4% wt. of solid residue is made of carbon, respectively. The model is also used to explain how the heating rate affects the temperature distribution inside the particle and how it shifts the peak of hydrogen release. Finally, the pyrolysis of two inhomogeneous wood samples — a beech twig with bark and a beech dowel with growth rings — are investigated. The bark can affect the pyrolysis rate, products, and flow pattern inside the particle. The growth rings do not have a considerable effect on the pyrolysis rate and products, but they have a significant impact on the flow pattern. This has an important implication for char conversion studies where the internal surface area and porosity field distribution have a significant effect on the gasification and oxidation rates.
Chapter
The chapter presents the results of experimental-analytical modeling of the surface forest fire dynamics and the process of forest fuel ignition when exposed to thermal radiation from the fire line. The regularities are established for the occurrence and spread of fires in natural ecosystems of the temperate climatic zone. Analytical solutions have been obtained that make it possible to predict the level of heat load on the soil cover of coniferous stands. The special computer program has been developed to calculate the heat load during fires. The methods of field and laboratory modeling revealed patterns of forest fuel heating and ignition depending on moisture content. A practice-oriented method is proposed to calculate the width of fire barriers that limit the spread of forest fires. The methods for creating fire barriers are proposed.
Article
Thermogravimetric curves of wood char oxidation consist of devolatilization and oxidation, described with a linear and a power-law rate reaction, respectively. The lack of measurement and control of the sample temperature in standard commercial thermogravimetric systems (STGA) can introduce serious deviations from the heating program, originated from heat and mass transfer limitations and reaction exothermicity. This study aims at quantifying the consequent effects on the estimated kinetic constants for beech, fir and spruce wood chars. A first set of measurements is based on a special purpose designed, home-made thermo-analyzer (HMTGA), permitting for an accurate sample temperature control and a rigorous kinetic regime. The second set makes use of a standard commercial thermobalance (STGA). It is found that for heating rates up to 10 K/min spikes in the rate curves disappear for 1 mg samples and the deviations on the activation energies become null or very small (maximum around 1-1.5 %), compared with the HMTGA data. However, the order of the oxidation reaction is always lower (by about 15 %). Improvements are not observed following further sample mass reduction.
Chapter
This chapter discusses the thermal runaway in alkaline batteries. It was shown that a lot of experimental data exists that contradict the generally accepted thermal runaway mechanism. On the basis of all the available experimental data, there was proposed the new thermal runaway mechanism. There it was shown that there are two processes of accumulation that step by step bring the nickel-cadmium batteries to the thermal runaway. First, this is a process of hydrogen accumulation inside of battery electrodes during their operation. Second, this is a process of dendrites accumulation on the cadmium electrodes of the batteries. It was experimentally proved (using thermal decomposition of sintered electrodes) that during Ni-Cd batteries long service life (more than five years), the hydrogen accumulation in large quantities takes place in a form of nickel hydrides in a sintered nickel matrix of oxide-nickel electrodes. In this chapter, it was deduced from experiments that an exothermic reaction in the thermal runaway process in alkaline batteries is the electrochemical reaction of atomic hydrogen recombination Hads Cd + Hads Ni → H2 ↑ (H2O + Hads + e− → H2 ↑+OH− on a cathode and Hads + OH− → H2O + e− on an anode). A rate-limiting step for this reaction on both a cathode and an anode is found to be a step of metal-hydrides disintegration. This electrochemical reaction proceeds at voltage 0.5–0.6 V on battery terminals. An analytical model of thermal runaway in alkaline batteries is proposed.
Article
Under unprecedented environmental crisis associated with greenhouse gas emission, biomass has attracted a great deal of attention due to renewable and carbon neutral nature. In this study, the premixed combustion of various types of wood and its derived syngases are examined for steady and oscillating sates. For this purpose, the poplar, birch, beech and pin sawdust woods and syngases composing of H2, CH4 and CO are considered. To model dust cloud combustion, a novel and comprehensive flame structure consisting of drying, two-step pyrolysis and homogeneous and heterogeneous reactions is proposed. Afterward, the governing equations and their appropriate boundary conditions are derived and solved analytically-numerically. The oscillating combustion is also modeled by exerting an external perturbation on the velocity field. The results indicate that due to the occurrence of heterogeneous reactions in wood combustion, the flame propagation velocity of wood is higher than that of syngases which contributes to high oscillations amplitude of syngases. When the mixture initial temperature changes between 300 and 550 K, the flame velocities of woods and syngases vary in the ranges of 0.4–0.7 m/s and 0.1–0.27 m/s, respectively. The maximum amplitude of temperature oscillation of syngases is approximately 8 times more than that of woods.
Article
In pyrolysis of biomass pellet, heterogeneity in char is almost inevitable, due to the intra-particle mass/heat transfer limitation. In this study, the effects of temperature (350–600 °C) and aspect ratio of a cylindrical sawdust pellet (Diameter = 6, 8, 12, or 16 mm) on the heterogeneity of char structure at radial and axial directions were investigated with a micro-Raman spectroscopy. Based on the spatial distribution of Raman band area ratios, heterogeneity index was proposed to quantify the degree of heterogeneity in char structures. Results show that the heterogeneity exists in both radial and axial directions and could be weakened by the increase of temperature or enlarging the variance between radius and height of the pellet through enhancing the average heat and mass transfer inside the pellet. The heterogeneity index of different biochar decreased with increasing surface-area-to-volume ratio. The char structures was the most heterogeneous (HI(AD/AG) = 5.399 × 10⁻⁵, HI(AD/A(Gr+Vr+Vl)) = 2.359 × 10⁻⁵) for the pellet with a diameter of 8 mm.
Article
This research focuses on the combustion of biomass char in fluidized beds of various particulate solids, which, under the conditions of the reaction, were either inert or capable of supplying oxygen to reactions. The latter were termed oxygen carriers. The solids used were SiO2, as an inert material, and three oxygen carriers: (1) Fe2O3 prepared from a natural pyrite ore, (2) CuO supported on mayenite, and (3) SrFeO3−δ strontium ferrite perovskite. Combustion experiments were undertaken by introducing a sample of partially devolatilized biomass (commercial “biochar”) to a hot bubbling bed (inner diameter of 30 mm), fluidized by a mixture of oxygen and nitrogen, then analyzing the composition of the off-gas and the burnout time of the char sample. In the temperature range investigated in this work (1023–1168 K), CuO and SrFeO3−δ but not Fe2O3 thermally decomposed, releasing gaseous O2 [so-called “chemical looping oxygen uncoupling” (CLOU)]. Hence, to make the combustion conditions comparable to various oxygen carriers, all experiments were performed using a fluidizing gas with a fixed partial pressure of O2 (pO2) of ∼0.015 bar. Despite the same nominal pO2, the occurrence of the oxygen uncoupling reaction increased the total net amount of O2(g) available in the process, affecting external mass transfer of O2 to the char particle and accelerating its rate of combustion. The time needed to totally combust 0.1 g of biochar particles in different beds at 1168 K followed the trend CuO < SrFeO3−δ < Fe2O3 ≈ silica sand. The difference in the performance of CuO and SrFeO3−δ was ascribed to the lower oxygen availability via CLOU in perovskite compared to copper oxide. Interestingly, combustion in the bed of Fe2O3 particles took a similar amount of time as combustion in the inert bed of SiO2, despite iron oxide playing an active role in the process. The finding is explained by Fe2O3 reacting with CO produced from incomplete char combustion, which results in the reduced oxide competing with char for O2(g) and effectively decreasing the local pO2.
Article
Thermochemical conversion provides promising approaches for utilization of agroforestry residues as energy sources in rural areas, such as decentralized biomass combustion and gasification. Understanding of the pyrolysis characteristics are crucial for the design of reactors and optimization of working conditions, but in these scenarios, utilization of centimeter-sized large fuel particles will bring challenges in predicting the evolution of pyrolytic products owing to the intraparticle secondary reactions. In this work, the product distribution of biomass pyrolysis was investigated in wide ranges of temperatures and particle sizes, and special attention was paid to the pyrolysis of centimeter-sized fuel particles under medium to high temperatures (500 °C – 900 °C). The yields of solid/liquid/gas-phase products were quantified, and the composition of tar and gas products were qualitatively and quantitatively evaluated, aiming at illustrating the effects of intraparticle secondary reactions. The results have shown that the differences between the product distribution of sawdust (<1 mm) and centimeter-sized wood cubes were significant over the whole temperature range, but the differences between wood cubes with varying sizes (1 cm, 1.5 cm and 2 cm) were dependent with the external temperature, indicating that the extent of intraparticle secondary reactions was simultaneously determined by external temperature and particle size. The evolution of tar composition indicated that the intraparticle secondary reactions could be divided into two distinctive steps. Increasing the particle size would firstly result in fast consumption of primary tar species and emergence of secondary tar species, while the second step would lead to the formation of simple phenols and aromatics, and large quantities of PAHs were released for centimeter-sized fuel particle under high temperatures (≥800 °C). Kinetic analysis further revealed that the first step was mainly transport controlled and sensitive to particle size, while the second step was jointly controlled by kinetics and transport, which appeared to be significant only if the particle size was large and simultaneously the temperature was sufficiently high.
Article
Char structure can reflect the pyrolysis characteristics and affect the efficiency of gasification and combustion processes, while biomass pellet size and shape are critical for the heat and mass transfer, which in turn influence greatly char structure. The aim of this study is to experimentally study and compare the effect of aspect ratio (diameter/length) on char structure during the pyrolysis of sawdust pellet. Cylindrical sawdust pellets with similar masses and volumes but different diameters (6, 8, 12, 16 mm) were pyrolysed at various temperatures. The chars were separated into two phases (liquid extraction, solid residue) via microwave-assisted extraction. Experimental results show that the pellet with a low aspect ratio had a large char yield because of intra-particle volatile-char interaction especially at low temperature, while there was an optimum aspect ratio due to the change of residence time. The pellet with a high aspect ratio had an intense polymerisation, resulting in the formation of fused aromatic rings in char and residue. By increasing aspect ratio, there was a lowest surface area. This means that less heat entered from surface, and low thermal conductivity caused a slow decomposition. Due to large heat and mass transfer residence, more aromatic molecules with small weight formed in extracts of char, especially at high temperature. Besides, an increase in temperature weakened the differences in structural features of the pellet char caused by different aspect ratios.
Article
Currently, there is a growing interest in various alternative energy sources due to the global energy scenario and rising crude oil prices. Renewable sources of energy like biomass can be exploited to produce energy-rich syngas. The biomass gasification process converts energy-rich solid fuel into syngas by partial combustion. In the present study, rice husk gasification using steam and, a mixture of steam and CO2 at temperatures ranging from 650°C to 750 °C and steam to biomass ratio of 0.5–2 is studied. Steam gasification enhances hydrogen production, and mixing with CO2 helps optimizing the H2/CO ratio. The study uses the Euler-Euler method in combination with kinetic theory granular of flow which is modeled using the computational fluid dynamics approach implementing user-defined functions for heterogeneous char reactions. The increased particle diameter harms the gasification performance due to the lower heating value of the syngas. As the steam to biomass ratio is increased, there is a positive effect on syngas quality, while temperature has a negative effect. The addition of CO2 increases the CO conversion in the syngas. The heterogeneous reaction rate vanishes close to zero after a height of 0.4 m, where all solid carbon is consumed.
Article
Over recent years, numerous studies have been concerned with recovering value-added products from sludge. Various methods have been used to prepare it as an adsorbent. Herein, a comprehensive and critical analysis of sources, pretreatments, activations, applications and environmental leaching risks of sludge-based activated carbon (SBAC) has been carried out. The characteristics and carbon-forming properties of sludges from different sources have been discussed, indicating that organic matter and minerals are the parts that favor carbon-forming. Comparing the BET surface area, pore volume and pore size distribution of SBACs obtained by different activation strategies, it is found that chemical activation can significantly increase the porosity compared to physical activation. By critically reviewing the co‑carbonization of waste sludge and other wastes, it has been concluded that factors such as temperature, raw material and doping ratio will determine the synergistic or antagonistic effect. The application of SBAC to absorb organic pollutants and heavy metals in water has been investigated. It has been found that the relationship between the particle size of pollutants and the pore size distribution of SBAC, and the interaction between pollutants and surface functional groups directly influence the adsorption effect of SBAC on environmental pollutants. Based on the summary of the recent research on SBAC, it is suggested that the research on SBAC should focus on improving chemical activation efficiency and the mechanism of the activation process. Moreover, it is proposed that the strategy of stabilizing heavy metals (such as adding metal oxides) should be actively studied in the future.
Article
In the search of new energy sources, this work aimed to investigate the pyrolysis of malt waste, the major by‐product generated from the brewing industry, to produce biochar and bio‐oil. The study also explored the effects of pyrolysis temperature and concentration of MgCl2 catalyst on the yields of bio‐oil, biochar and pyrolytic gas. The pyrolysis products were analyzed using Fourier transform infrared spectroscopy. The effects of the studied variables on the yields and quality of the pyrolysis products were quantified using regression technique. It was found that the use of MgCl2 favored dehydration reactions and generated biochar and bio‐oil with less oxygen and greater calorific value, thus improving their use as a fuel. In addition, the MgCl2 accelerated the formation of intermediate compounds at low temperatures, changed the reaction pathways and decreased the reaction complexity, consequently reducing the activation energy value and the order of reactions. The catalytic pyrolysis of malt waste was evaluated. The kinetic study revealed a great reduction in the activation energy during catalytic degradation. The results provided by the 32 factorial experimental design evaluated the effect of temperature and MgCl2 concentration on the product yields using Response Surface Methodology (RSM). The semi‐quantitative FT‐IR analysis identified the composition of biochar, acid extract and bio‐oil. In conclusion, the conditions that maximized C sequestration along biochar and bio‐oil production, as well as their properties, were successfully verified.
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A co-current moving bed gasifier with internal recycle and separate combustion of pyrolysis gas has been developed with the aim of producing a design suitable for scaling-up downdraft gasifiers while maintaining a low tar content in the producer gas. Using wood chips with a moisture content of 7–9 wt% (db) as a fuel at a rate of 20 kg h−1, this system produced a gas with a heating value of 4500 kJ ms−3 and a very low tar content of < 0.1 gms−3.
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A detailed mathematical model is presented for the temporal and spatial accurate modeling of solid-fluid reactions in porous particles for which volumetric reaction rate data is known a priori and both the porosity and the permeability of the particle are large enough to allow for continuous gas phase flow. The methodology is applied to the pyrolysis of spherically symmetric biomass particles by considering previously published kinetics schemes for both cellulose and wood. A parametric study is performed in order !o illustrate the effects of reactor temperature, heating rate, porosity, initial particle size and initial temperature on char yields and conversion times. It is observed that while high temperatures and fast heating rates minimize the production of char in both reactions, practical limits exist due to endothermic reactions, heat capacity and thermal diffusion. Three pyrolysis regimes are identified: 1) initial heating, 2) primary reaction at the effective pyrolysis temperature and 3) final heating. The relative durations of each regime are independent of the reactor temperature and are approximately 20%, 60% and 20% of the total conversion time, respectively. The results show that models which neglect the thermal and species boundary layers exterior to the particle will generally over predict both the pyrolysis rates and experimentally obtainable tar yields. An evaluation of the simulation results through comparisons with experimental data indicates that the wood pyrolysis kinetics is not accurate; particularly at high reactor temperatures.
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The working hypothesis for the study was that the main part of the chlorine in biomass is in an inorganic form and therefore should not vaporize appreciably below the melting point of the corresponding salt (around 700 °C) because the vapor pressure over solid salt is negligible. In the study, biomass fuels (sugarcane trash, switch grass, lucerne, straw rape) were subjected to pyrolysis in a flow of nitrogen, and the weight of the residue and its chlorine content were measured and compared to the original fuel. Contrary to the hypothesis, the results showed that during pyrolysis of biomass 20−50% of the total chlorine evaporated already at 400 °C, although the majority of the chlorine was water soluble (in grass 93%) and therefore most probably ionic species. At 900 °C, 30−60% of the chlorine was still left in the char. At 200 °C less than 10% of chlorine had evaporated from the fuel, indicating that the chlorine is not associated with water. Another result was that there was no significant difference in the chlorine release between biomass and synthetic waste, i.e., a mixture of organic and inorganic chlorides. These results are contradictory with the starting hypothesis and can therefore have new implications for the use of these fuels in combustion and gasification processes.
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Sugar cane bagasse, wheat straw, pine and cotton wood pyrolysis was studied by TGA in argon at heating rates of 5 and 20°C/min. The DTG (-dm/dt) peaks associated with the components of an untreated plant material are relatively wide and strongly overlap each other. A reduction in the amount of inorganic ions in the samples by simple water or dilute acid washing procedures resulted in sharper peaks with a better separation. The thermal decomposition of the major biomass components was described, more or less formally, by first order reactions and the DTG curves of the biomass samples were approximated by a linear combination of first order reactions. Good fits between the calculated and the experimental data and good reproducibility of the model parameters were achieved. The kinetic model applied here may serve as a starting point to build more complex models capable of describing the thermal behavior of plant materials during a thermal or thermochemical processing or burning. Theoretically, there is also a possibility to utilise this sort of calculation in the quantitative analysis of the cellulose and hemicellulose content of the lignocellulosic materials.
Article
The pyrolysis of biomass is a thermal treatment which results in the production of char, liquid and gaseous products. The aim of this paper is the study of the influence of kinetic and diffusion phenomena on the pyrolysis of biomass particles. In our aboratory the pyrolysis process has been studied experimentally using thermogravimetric techniques and different scales of apparatus. Experimental data suggest that the pyrolysis of fine particles can be controlled by kinetics. The rate of pyrolysis of biomass can be well represented by the sum of the corresponding rates for the main biomass components. The effect of particle size has also been studied by measuring the weight-loss rate. For particles below 1 mm in diameter the process is controlled by kinetics, for larger particles the process is controlled by both heat transfer and primary and secondary pyrolysis reactions. As the temperature and the particle size increase the relative influence of transfer phenomena and secondary reactions increases. The temperature profiles inside the particles during pyrolysis were also measured.
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A 3 kg/h ablative pyrolysis reactor and a 1.5 kg/h fluid bed reactor were operated using pine wood as the feedstock over a temperature range of 450–600°C. Mass balances and product analyses were performed and product comparisons made. A similar gas/vapour product residence time of around 1 s was used to reduce differences. Product yields followed the same general trends with a maximum organics liquid yield around 500–515°C for both reactors (59.4 wt% organics at 515°C and 1.19 s residence time in the fluid bed reactor and 62.1 wt% organics at 502°C and 1.1 s residence time for the ablative reactor]. Char yields increased for the fluid bed reactor above 515°C, and also in the ablative pyrolysis reactor. The volatile content of the char products were higher for the ablative, compared to the results for the fluid bed chars which showed a continual rapid decrease. Water yields were similar in the range of 11–16 wt%. Gas yields were markedly lower in the ablative pyrolysis reactor suggesting a less severe environment for the vapour products. The gaseous product composition variation with temperature in the fluid bed suggests that secondary vapour cracking is more prevalent in the fluid bed than the ablative pyrolyser.
Chapter
Upon heating, biomass materials undergo solid phase pyrolysis at relatively low temperatures (> 300 ºC), forming reactive volatile matter, a few permanent gas species and solid char. Unlike the various coals and peats, biomass materials typically lose 70% or more of their weight by the solid phase pyrolysis reactions. This transformation of the bulk of the biomass material from the solid to the vapor phase suggests the important role of vapor phase chemistry in the pyrolysis of biomass materials. Recognizing the highly reactive nature of the major constituents of the volatile matter, the significance of the vapor phase chemistry becomes even more apparent.
Article
Recent studies and information on principal thermal reactions and products of cellulosic materials, and some of the proposed thermal conversion processes are reviewed to indicate the future possibilities and promises of this approach.
Article
Many types of chemical pathways aimed at representing the primary process of biomass degradation have been published. These models include or ignore the possibility of the existence of an intermediate “Active” species or state. The purpose of this paper is to gather theoretical results and experimental observations intended to open the discussion on the possible existence and nature of such an intermediate. The results of the modelling of the chemical and thermal behaviour of biomass undergoing a pyrolysis decomposition are first given. Simple experimental and visual observations associated with theoretical considerations based on heat transfer measurements lead then to the conclusion that the overall reaction is similar to a fusion with production of an intermediate liquid species. From kinetic rate constants derived from literature, it appears that it is not necessary to take into account such a liquid in thermogravimetric analysis (TGA) experiments, but that it cannot be ignored in high temperature ablative pyrolysis conditions. At the end of the paper, a discussion is conducted on the possible chemical natures of these liquids, the evolved vapours and the condensed pyrolysis oils formed in a pyrolysis process. It is concluded that the primary liquids could be composed of dimers and higher oligomers derived from cellulose and lignin, while the vapours would be mainly monomers and monomer fragments from the cracking of oligomers in the liquid phase.
Chapter
A transient, one-dimensional model which can simulate drying and pyrolysis of moist wood is presented. The porous wood is divided into four phases: solid, bound water, liquid water and gas phases. Conservation equations for energy and mass together with Darcy’s law for velocity and algebraic equations for the transport properties and physical properties are presented. The drying model is based on equilibrium between water vapor and bound or liquid water in the porous wood. For the thermal degradation process, two reaction schemes including a single one-step global and a multiple competitive reaction model which have been proposed in the literature, are included. A comparison between the two pyrolysis models has been made on dry wood and the results reveal that for the multiple reaction model, the heating rate and pyrolysis time have great influence on the ultimate char, tar and gas yields calculated. Simultaneously drying and pyrolysis of large wood particles are simulated. The effect of moisture content on the pyrolysis time is presented together with characteristic profiles for temperature, pressure and moisture distribution inside the particle. A temperature plateau can be observed at about 100°C where evaporation and condensation of liquid water takes place. The simulations show that the in-depth moisture content increases and exceeds the initial moisture content before evaporation. The reason for this increase is that when water evaporates in the front, some of it will be transported by convection and diffusion into the colder region and condensed.
Article
A normative review of the literature describing the products, mechanisms, and rates of lignin and whole biomass pyrolysis is presented. The role of a complex sequence of competing solid- and vapor-phase pyrolysis pathways is elucidated.
Article
The liquid products (tars or sirups) obtained from the fast pyrolysis of cellulosics show a wide variation in composition depending on the cellulosic feedstock used. Native cellulose in wood gives significant yields of hydroxyacetaldehyde and other low molecular weight oxygenated compounds but low yields of anhydrosugars, while highly altered micro-crystalline cellulose gives the reverse. Experimental results from fluidzed bed fast pyrolysis are given for poplar wood and for a number of types of cellulose produced by different processes. The effect on product nature and yields as a result of different pretreatments of the wood or cellulose before pyrolysis is also reported. From these observations, as well as from the variation of product yields with temperature for one cellulose product, possible mechanisms for the primary decomposition of cellulose are proposed. Two major parallel pathways appear to account for the yields of major products. The content and nature of inorganic salts and the degree of polymerization of the cellulose play an important role in determining the relative importance of these two decomposition pathways.
Article
A pyrolysis kinetics model is presented which can be used for the prediction of pyrolysis oil yields for oak in an entrained-flow reactor. The parameters in the model were determined by a nonlinear least-squares computer code and experimental results. An interpretation of the model predictions is included. The maximum oil yield obtained experimentally was 51%. The model predicts that a maximum oil yield of 63% is possible at a temperature of 550 degree C (the highest temperature run to date) at a much higher inlet gas rate than has been used.
Chapter
When wood is heated at elevated temperatures, it will show a permanent loss of strength resulting from chemical changes in its components. The thermal decomposition can start at temperatures below 100°C if wood is heated for an extended period of time. Figure 1 shows that wood heated at 120° loses 10% of its strength in about one month, but i t takes only one week to obtain the same loss of strength if it is heated at 140° (1). Heating at higher temperatures gives volatile decomposition products and a charred residue. The pyrolytic reactions and products control the combustion process and relate to the problems of cellulosic fires, chemical conversion of cellulosic wastes and utilization of wood residues as an alternative energy source. In our laboratory, the pyrolytic reactions of wood and its major components have been investigated by a variety of analytical methods. Thermal analysis of cottonwood and its
Article
A heat radiation reactor was used to study the mechanism of cellulose rapid pyrolysis in the present paper. Combined with gas chromatography-mass spectrometry analysis on bio-oil, experimental results showed that the production rate of hydroxyacetaldehyde and 1-hydroxy-2-propanone, as well as their proportions in bio-oil, increased with the reaction temperature in the case of short gas residence time. The formation of the above two products was shown to be competitive with levoglucosan formation from active cellulose. In addition, a modified cellulose pyrolysis model based on the Brodio-Shafizadeh model was proposed to describe this competitive phenomenon. Major products' formation was simulated with this modified model, which was in good agreement with the experimental results.
Article
The influence from structural changes, heat transfer properties of dry wood and pyrolysis mechanism on the pyrolysis of large wood particles were studied. Measurements of temperature distribution and mass loss were performed on cylindrical samples of dry birch wood during pyrolysis in an inert atmosphere at 700°C. A model of wood pyrolysis was modified to include structural changes. Comparisons of measurements and model simulations show that the inclusion of a shrinking model reduces the time of pyrolysis substantially. The varying interior heating rate was found to influence the choice of pyrolysis mechanism. Of four pyrolysis mechanisms found in literature, only one was found to be in agreement with the measurements.
Article
This paper examines the effects of intraparticle heat and mass transfer on the devolatilization of millimeter-sized biomass particles under conditions similar to those found in commercial coal-fired boilers. A computational model is presented that accounts for intraparticle heat and mass transfer by diffusion and advection during particle heating, drying, and devolatilization. To evaluate the model, devolatilization experiments under high-temperature and high-heating rate conditions were conducted using the Multifuel Combustor at Sandia National Laboratories. Measurements of mass-loss and changes in particle size for millimeter-sized alfalfa and wood particles are presented as a function of reactor residence time. For millimeter-sized particles, both fuels completely devolatilized in approximately 1 s with rapid initial mass loss. The total volatile yield of the wood was 92% on a dry, ash-free basis, significantly higher than that reported by a standard ASTM test, indicating dependence of the ultimate yield on local conditions. Particles for both fuels shrink significantly and become less dense during devolatilization. The comprehensive model accurately predicts the devolatilization behavior of millimeter-sized biomass particles; these measurements could not be reproduced with a simple lumped model that ignores intraparticle transport effects. The comprehensive model is used to examine the effects of particle size and moisture content on devolatilization under conditions representative of those found in coal boilers. Biomass particles of radii up to 2 mm and moisture content up to 50% are considered. As expected, intraparticle heat and mass effects are more significant for larger particles. These effects can significantly delay particle heating and devolatilization; for example, intraparticle effects delay the heating and devolatilization of millimeter-size particles by as much as several seconds for a particle with a 1.5-mm radius compared to predictions of a lumped model. This delay is significant considering the short residence times of commercial boilers and should be accounted for in computational models used to evaluate the effects of biomass-coal cofiring on boiler performance.
Article
We present here a decoupling technique to tackle the entanglement of the nonlinear boundary condition and the movement of the char/virgin front for a thermal pyrolysis model for charring materials. Standard numerical techniques to solve moving front problems — often referred to as Stefan problems — encounter difficulties when dealing with nonlinear boundaries. While special integral methods have been developed to solve this problem, they suffer from several limitations which the technique described here overcomes. The newly developed technique is compared with the exact analytical solutions for some simple ideal situations which demonstrate that the numerical method is capable of producing accurate numerical solutions. The pyrolysis model is also used to simulate the mass loss process from a white pine sample exposed to a constant radiative flux in a nitrogen atmosphere. Comparison with experimental results demonstrates that the predictions of mass loss rates and temperature profile within the solid material are in good agreement with the experiment. Copyright © 1999 John Wiley & Sons, Ltd.
Article
Biomass pyrolysis studies were conducted using both a thermogravimetric analyser and a packed-bed pyrolyser. Each kind of biomass has a characteristic pyrolysis behaviour which is explained based on its individual component characteristics. Studies on isolated biomass components as well as synthetic biomass show that the interactions among the components are not of as much significance as the composition of the biomass. Direct summative correlations based on biomass component pyrolysis adequately explain both the pyrolysis characteristics and product distribution of biomass. It is inferred that there is no detectable interaction among the components during pyrolysis in either the thermogravimetric analyser or the packed-bed pyrolyser. However, ash present in biomass seems to have a strong influence on both the pyrolysis characteristics and the product distribution.
Article
The effects of cations on the yields of char, tar, light oils, and total gases from rapid pyrolysis of beech wood were studied. Raw wood, acid washed wood, and wood impregnated with potassium, sodium, and calcium cations were pyrolyzed in 1 atm pressure of helium at 1000°C s−1 heating rate to a peak temperature of ≈ 1000°C. Experiments were carried out in an electrical screen heater reactor, and the yields of products were determined as a function of pyrolysis peak temperature. Acid washed wood samples gave the highest tar yield (about 61% by weight of the original wood), whereas wood samples impregnated with potassium or sodium cations gave the lowest yield of tar (32 wt%). The char yield from acid washed wood samples was lower (about 6 wt%), and it was higher for raw wood and for wood samples impregnated with different cations (10–15%). The maximum gas yield was lower at ≈ 34 wt% for acid washed wood and much higher (≈ 58 wt%) for the wood samples impregnated with potassium and sodium cations. These results, as expected, confirm the marked catalytic effects of cations on the post-pyrolysis cracking reactions of tar (the major product of wood pyrolysis) and the formation of char and gaseous products via cracking reactions of tar. In all these cases, sodium and potassium cations showed a stronger effect than calcium cations. The tar molecular weight was measured for wood samples impregnated with different cations. Tar molecular weight decreased with addition of cations to the wood particles, whereas it remained relatively constant with pyrolysis temperature. The tar molecular weight dropped from about Mw = 300 amu and Mn = 155 amu for raw and acid washed woods to about Mw = 190 amu and Mn = 100 amu for woods impregnated with potassium or sodium cations.
Article
A Setaram DSC in conjunction with stainless steel pressure vessels was used to investigate the effects of pressure and purge gas flow rate (gas phase residence time) on the heat demands of cellulose pyrolysis. High pressure and low flow rate reduce the heat of pyrolysis and increase char formation. Experiments were conducted to investigate the pyrolysis reactions of anhydrocellulose and levoglucosan, the two major intermediate products in cellulose pyrolysis. Separate models for the degradation of each intermediate were postulated and combined to form a detailed mechanistic model for cellulose pyrolysis. The model explains all the observed effects of pressure and flow rate.
Article
Rice hulls were pyrolyzed in a thermogravimetric analyzer in a helium atmosphere to determine the kinetic parameters of devolatilization reactions. The pyrolysis experiments were conducted by heating rice hulls from room temperature to 1173 K at constant heating rates of 3, 10, 30, 60, and 100 K/min. The global mass loss during rice hull pyrolysis was successfully simulated by a combination of four independent parallel reactions, the decompositions of four major components in rice hulls: moisture, hemicellulose, cellulose, and lignin. The activation energy for the decomposition of the nonmoisture components was in the order cellulose > hemicellulose > lignin. It was also found in the present study that the pyrolytic behaviors were significantly influenced by water wash prior to pyrolysis. The water wash elevates the peak temperature and the activation energy for the decomposition of each component of rice hulls. The volatile yields resulting from cellulose and hemicellulose decompositions during rice hull pyrolysis increase due to the water treatment, whereas those from lignin decomposition and the char yield decrease.
Article
The homogeneous vapor phase cracking of newly formed wood pyrolysis tar was studied at low molar concentrations as a function of temperature (773 - 1.073 K), at residence times of 0.9 - 2.2 s. Tar conversions ranged from about 5 to 88%. The tars were generated by low heating rate (0.2 K/s) pyrolysis of --2 cm deep beds of sweet gum hardwood, and then rapidly conveyed to an adjacent reactor for controlled thermal treatment. Quantitative yields and kinetics were obtained for tar cracking and resulting product formation. The major tar conversion product was carbon monoxide, which accounted for over two-thirds of the tar lost at high severities. Corresponding ethylene and methane yields were each about 10% of the converted tar. Coke formation was negligible and weight-average tar molecular weight declined with increasing tar conversion.
Article
Improved experimental techniques are described, using a wire mesh reactor; for determining the pyrolysis yields of lignocellulosic materials. In this apparatus pyrolysis tars are rapidly swept from the hot zone of the reactor and quenched, secondary reactions are thereby greatly diminished. Particular emphasis is placed upon the measurement of the pyrolysis yields for sugar cane bagasse, an abundant agricultural waste product. The role of the important pyrolysis parameters, peak temperature and heating rate, in defining the ultimate tar yield is investigated, with the value for bagasse being 54.6% at 500 C and 1,000 C/s. The pyrolysis yields, under similar conditions, of another biomass material, silver birch, are also reported and compared to those of bagasse.
Article
In recent years there has been a growing interest in using wood, bark and foliage for chemical biomass conversion studies.1 The reasons are understandable since forests represent one of the largest sources of renewable biomass still available to mankind. Also, the Forest Product Industries provide a constant, collected source of potential thermochemical conversion material such as tops, limbs, bark and foliage not required for lumber or pulp. This potential will increase dramatically if plans to introduce whole tree logging materialize. Unfortunately, many scientists have been attracted to this potential biomass who are unfamiliar with the wide variation among and between tree species. To many wood is wood and they make little attempt to define the sample on which valuable scientific research is done. Borrowing a sentence from the Basic Coal Sciences Project Advisory Report2 and substituting wood for coal, the following statement emerges and describes the current situation concisely: ‘Considerable basic research has been done on a wide range of wood samples for various purposes, yet much of this previous research cannot be correlated since little, if any comparisons can be drawn from the samples used’. The Estes Park conference unanimously endorsed the need for reviewers and authors to be aware of tree variability and to define all research samples in such a way that other scientists may be able to calibrate and correlate their own research results.
Article
Seeking to systemalically identify and organize the physical and chemical properties of biomass particles for combustion in furnaces, an attempt is made here to theoretically describe the temporal change in mass of a burning particle of an organic solid. The development involves a series of simple models to highlight the mechanisms involved, the physical and chemical properties of concern and the expected results. Although many simplifying assumptions are made, the properties identified, the parameters which evolved and the final functional form of the results are expected to becorrect.
Article
A mathematical model based on unreacted-core shrinking model is developed to describe the pyrolysis phenomena of the cellulosic materials in the temperature range of 700–1470 K. The relative importance of each model parameter is studied by applying the sensitivity analysis. The heat transfer control region and kinetic reaction control region are obtained from the developed model. The shift of controlling mechanism is dependent on the particle size and the wall temperature. The effect of heat of reaction on the temperature of the particle is also discussed.
Article
Single, thermally thick particles of lodgepole pinewood were pyrolyzed under well-defined conditions of industrial importance. Particle thickness, heating level, moisture content, density, and grain axis relative to one-dimensional heating were varied using a Box-Behnken experimental design. Gross product fractions, as well as components therein, were measured and the batch yields were correlated with second-order polynominals. The empirical equations correlating the batch yields, together with their prediction uncertainties, are presented and are suitable for use in simulations of wood combustion and thermal conversion. Comparison of large particle pyrolysis product distributions to other studies of small-particle pyrolysis yields shows the trends with particle size to be consistent. Tar yield minima depend on both particle size and heating rate. Gas yield is dependent on both particle size and heating intensity. Because some process controllables were found to alter product yields from large particles in a multiplicative way, rather than an additive way, suggestions for future experiments are made.
Article
Thermogravimetric data on the devolatilization rate of beech wood are re-examined with the aim of incorporating the effects of high heating rates (up to 108Kmin−1) in the global kinetics. The mechanism consisting of three independent parallel reactions, first-order in the amount of volatiles released from pseudo-components with chief contributions from hemicellulose, cellulose and lignin, is considered first. It is found that the set of activation energies estimated by Gronli et al. [M.G. Gronli, G. Varhegyi, C. Di Blasi, Ind. Eng. Chem. Res. 41 (2002) 4201–4208] (100, 236 and 46kJmol−1, respectively) for one slow heating rate results in very high deviations between predicted and measured rate curves. The agreement is significantly improved by a new set of data consisting of activation energies of 147, 193 and 181kJmol−1, respectively. In this case, the overlap is reduced between the reaction rates of the three pseudo-components whose chemical composition is also modified. In particular, instead of a slow decomposition rate over a broad range of temperatures, the activity of the third reaction is mainly explicated along the high-temperature (tail) region of the weight loss curves. The performances of more simplified mechanisms are also evaluated. One-step mechanisms, using literature values for the kinetic constants, produce large errors on either the conversion time (activation energy of 103kJmol−1) or the maximum devolatilization rate (activation energy of 149kJmol−1). On the other hand, these parameters are well predicted by two parallel reactions, with activation energies of 147 and 149kJmol−1.
Article
A comparison between the thermal decomposition of almond shells and their components (holocellulose and lignin) was carried out, considering the yields of the most important products, under flash conditions, and the decomposition kinetics.The yields of the main gaseous products obtained in the fast pyrolysis of almond shells can be reproduced from the yields obtained with holocellulose and lignin. The best results were obtained with CO, water and CO2. The differences were greater with the minor hydrocarbons, CH4, C2H6, C2H4, etc.The kinetics of the slow thermal decomposition (TG-DTG) of almond shells cannot be reproduced by the sum of lignin and holocellulose. The cellulose from almond shells decomposes at lower temperatures than almond shells, and the behavior of isolated lignin is very different from that found when it forms part of the raw material, proving the importance of the interactions between its components.
Article
Drying and devolatilization are studied at combustion temperatures. The surface temperature of particles at the end of drying can significantly exceed the temperature when devolatilization starts, implying that drying and pyrolysis may partly overlap. Devolatilization is controlled by heat transfer, when the particle size is large. The critical particle size at which heat transfer dominates chemical kinetics is discussed. A model for calculating the intrinsic rate of generation of volatiles in the regime of heat transfer control is presented. A novel isotherm migration method is used for the computation of simultaneous drying and pyrolysis inside a fuel particle. It applies to the study of heat transfer in a one-dimensional geometry with moving phase-change boundaries, internal fluid flow and mass generation, including steep temperature and density profiles, as frequently encountered in combustion.
Article
In this paper, the weight loss of four different woods during vacuum pyrolysis at constant temperature and at constant heating rate are reported. Based on these results, an empirical model of the weight loss rate as a function of temperature has been developed. The model assumes that wood is composed of three major components: cellulose, lignin, and a mixture of hemicellulose and volatiles. Under vacuum conditions, it is also assumed that the pyrolysis of these components proceeds independently of the others. The resulting kinetic parameters can be used to predict volatilization rates of wood as a function of temperature in a vacuum. The model may also be used to estimate the quantities of each of the main components initially present in an unknown wood sample.
Article
A lumped-parameter kinetic model is applied to simulate the pyrolysis of lignocellulosic particles, exposed to a high temperature environment. Physical processes account for radiative, conductive and convective heat transport, diffusion and convection of volatile species and pressure and velocity variations across a two-dimensional (2-D) , anisotropic, variable property medium. The dynamics of particle degradation are found to be strongly affected by the grain structure of the solid. A comparison is made between the total heat transferred to the virgin solid (conduction minus convection) along and across the grain. Notwithstanding the lower thermal conductivities, because of the concomitant slower convective transport (lower gas permeabilities) , the largest contribution is that across the solid grain. The role played by convective heat transport is successively less important as the particle size is increased. Finally, the 2-D and the widely applied one-dimensional (1-D) predictions are compared.
Article
Pyrolysis experiments in a thermogravimetric analyser and in a muffle furnace were carried out with spruce and beech wood. The particle size of the samples of spruce wood was varied in the range 0.5–20 mm and the heating rate was varied in the range 5–60 K/min. Additionally, drop-in experiments in the muffle furnace were carried out with both spruce and beech wood. These experimental data were compared with the results from calculation of pyrolysis of ‘large’ particles with the simulation program parsim. Agreement could only be obtained when the tar decomposition outside of the particle was taken into account. The pre-exponential factor and the ultimate yield for cracking of tar from beech wood are given.
Article
This work deals with the kinetic analysis of data obtained in thermobalance. It consists of a review of kinetic models used for material decomposition, and also of the methods used for the analysis. The topics presented comprise numerical problems related with kinetic analysis, best conditions for a kinetic run, discussion about correlation vs. actual models, nth order models, more complex models (models using a great number of reactions, models using various fractions), calibration of the temperature, position of the thermocouple, sample mass and particle size. Other topics treated are the validation of kinetic models using MS data and the different models available for kinetic studies in thermobalance.
Article
Release of volatiles of non-spherical pine wood particles was analysed by means of continuous measurements of the CO2 and O2 concentrations obtained after the complete combustion of the volatiles and from flame extinction times. The effect of the atmosphere used for devolatilisation was tested. The volatiles' evolution was nearly identical using air or N2 as fluidising gas. The devolatilisation times increased with increasing the equivalent particle diameter, but there was an important scattering in the results. The data dispersion greatly decreased when the shape factor of the wood particles was considered. The devolatilisation times were fitted to a power-law relation replacing the particle diameter by the equivalent particle diameter multiplied by the shape factor. The effect of the moisture content was studied by analysis of the devolatilisation process of pine wood particles of the same size and different moisture contents (0–50%). As the moisture content of the wood particles increased the devolatilisation rate of combustible volatiles decreased and was more uniform along the devolatilisation time.
Article
The catalytic effect of pH-neutral inorganic salts on the pyrolysis temperature and on the product distribution was studied by fractionated pyrolysis followed by GC/MS and GC/FID and by thermogravimetric analysis (TGA) of cold-water-washed hornbeam wood. Sodium and potassium chloride have a remarkable effect on the pyrolysis temperature and on the product distribution, whereas calcium chloride only changes the low temperature degradation of hornbeam wood and the product distribution is nearly unchanged compared with water-washed hornbeam wood. All studied potassium salts (KCl, KHCO3, and K2SO4) decrease the amount of levoglucosan the order of magnitude being dependent on the anion: chloride has a more pronounced effect than sulphate, and sulphate a more pronounced effect than bicarbonate. The thermal degradation of three different wood species (hornbeam, walnut and scots pine) was investigated by analysis of thermogravimetric/mass spectrometric pyrolysis. Commonly used model substances for the main components of wood, like xylan, pure cellulose or filter pulp, were found to be unreliable for the evaluation of formal kinetic parameters that are able to describe the pyrolysis of wood. A method for the individual evaluation of formal kinetic parameters for the main components of wood was used, that uses specific ion fragments from lignin degradation products to study the lignin degradation. Coniferous lignin is thermally more stable than deciduous lignin, and the latter produces smaller char yields. The differences in wood species mainly result in different degradation rates for the lignin and for the early stages of the hemicellulose degradation.
Article
A kinetic study of the pyrolysis of municipal solid waste (MSW) in a fluidized bed reactor was carried out. The MSW pellets are discharged onto the fluidized sand bed; in the upper part of the reactor the volatiles evolved from primary reactions underwent secondary cracking reactions. A correlation model was applied to simulate the primary and secondary reactions as well as the heat transfer process. The experimental yields of the total gases obtained in 49 runs performed at 700, 750, 800 and 850 °C fitted satisfactorily using a flexible simplex method. The values of the kinetic parameters of secondary reaction, the heat transfer coefficient from the bed to the sample and the ratio “secondary gas yield/primary tars yield” were optimised. The values of the secondary kinetic parameters, which showed a great inter-relation with those of the primary reactions, were within the range of the values proposed in literature for other biomass tar cracking.
Article
A kinetically based prediction model for the production of organic liquids from the flash pyrolysis of biomass is proposed. Wood or other biomass is assumed to be decomposed according to two parallel reactions yielding liquid tar and ( gas + char) The tar is then assumed to further react by secondary homogeneous reactions to form mainly gas as a productThe model provides a very good agreement with the experimental results obtained using a pilot plant fluidized bed pyrolysis reactorThe proposed model is shown to be able to predict the organic liquid yield as a function of the operating parameters of the process, within the optimal conditions for maximizing the tar yields, and the reaction rate constants compare reasonably well with those reported in the literature